/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.update.processor;

import org.apache.solr.core.SolrCore;

import org.apache.solr.common.SolrInputField;
import org.apache.solr.request.SolrQueryRequest;
import org.apache.solr.response.SolrQueryResponse;

import java.util.Collection;

/**
 * Base class for processors that want to mutate selected fields to only keep a
 * subset of the original values.
 * 
 * @see #pickSubset
 */
public abstract class FieldValueSubsetUpdateProcessorFactory extends
		FieldMutatingUpdateProcessorFactory {

	@Override
	public final UpdateRequestProcessor getInstance(SolrQueryRequest req,
			SolrQueryResponse rsp, UpdateRequestProcessor next) {
		return new FieldMutatingUpdateProcessor(getSelector(), next) {
			protected SolrInputField mutate(final SolrInputField src) {
				if (src.getValueCount() <= 1)
					return src;

				SolrInputField result = new SolrInputField(src.getName());
				result.setValue(pickSubset(src.getValues()), src.getBoost());
				return result;
			}
		};
	}

	/**
	 * Method subclasses must override to specify which values should be kept.
	 * This method will not be called unless the collection contains more then
	 * one value.
	 */
	protected abstract Collection<Object> pickSubset(Collection<Object> values);

}
